Picture transmitting system



July 14, 1936. A; BA.. EY v 2,047,817

PICTURE TRANSMITTING SYSTEM Filed Dec. 24, 1924 ZSheet-s-Sheet 1 W |I ii a A i 5 Q F R; I III R, I N) a3 5 INVENTOR flflwa'ley;

ATTORNEY.

July 14, 1936. BA|LEY 2,047,817

' PICTURE TRANSMITTING? SYSTEM Filed Dec. 24, ,1 4 2 Sheets-Sheet 2 5 W gs? W941 ATTORNEY Patented July 14, 1936 PATENT OFFICE PICTURE TRANSMITTING SYSTEM Austin Bailey, Freehold, N. J. assignor to American Telephone and Telegraph Company, a cor poration of New York Application December 24, 1924, Serial No. 757,871 14 Claims. (01. 178-6) My invention relates to carrier current transmission and an object is to provide an improved method andsystem of carrier current transmission especially adapted for picture and image transmission and for radio sending and receiving. Another object of my invention is to provide for transmitting a picture or other image by modulation of a current in such a way that the operation will not be unfavorably affected by variable transmission losses. In accordance with the preferred form of my invention provision is made for sending a picture or other image by interrupting a current at a varying frequency corresponding to the shade of successive picture elements, operating a receiving means in accordance with this variable frequency and limiting the amplitude of response of the receiving means so that variations in the amplitude of the current will give no unfavorable effect. These and various other objects of my invention will become apparent on consideration of an example of practice in accordance therewith which I have illustrated in the accompanying drawings and will now proceed to describe in the following specification. It will be understood that this specification relates to this particular example of the invention and that the invention will be defined in .the appended claims.

Referring to the drawings, Figure 1 is a diagram of a radio picture sending station embodying my invention; Fig. 2 is a diagram of the corresponding receiving station; and Fig. 3 is a diagram showing the nature of the picture record at the receiving station.

Light from the source II passing through the lens i2 is reflected by the mirror I3 within the open-ended glass drum l4 supported on the shaft Ill. The light from the mirror I3 is focused near the surface of the drum M, round which the picture to be transmitted is wrapped in the form of a semi-transparent film. The light passing through the spot of the film across its path goes through the lens I5 and is focused in the photoelectric cell It.

The drum I4 is rotated by the synchronous motor l9, and the supporting shaft I! has screwthreaded engagement with the frame l8 so that as the drum l4 rotates it is also advanced slowly, and the elemental area of the film lying in the path of the beam of light traces a helical course on the film. Accordingly the light to the photoelectric cell I 6 varies according to the shade of successive elementary areas of the film in helical order.

The current in the circuit of the photoelectric cell It varies according to the quantity of light and actuates the galvanometer 20 whose moving member carries one plate of the adjustable condenser 2l. Thus the capacity of the condenser 2i is adjusted to correspond to the degree of shade in the successive elements of the picture.

The condenser 2i forms part of an oscillatory circuit which also comprises the condensers 22 and 25 and the coils 23 and 24. Condenser 22 is made adjustable so that when no light falls on the cell IS the beat frequency between the two oscillators 29 and that including tube 26-2'l can be made zero and no signal (or a long dash) will be transmitted. The oscillation frequency of the oscillatory circuit just referred to will vary ac cording to the adjustment of the condenser 2i, and an electromotive force of this frequency will be impressed on the grid 26 of the audion whose plate is El. Accordingly there will be a corresponding oscillatory current developed in the plate circuit and applied through the transform- .er primary winding 28.

An oscillation generator 29 sends current of constant frequency through the primary winding 30, and both primaries 28 and 30 cooperate with the same secondary 69 so that both frequencies are put into the demodulator 3i. The direct current in the plate circuit of the demodula'tor 3i is a current varying in intensity at a frequency corresponding with the variation of the capacity of the condenser 2|, that is, in correspondence with the degree of shade in the successive elements of the picture on the drum M. Accordingly for one extreme shade the relay 32 will operate rapidly to open and close its contact 33, and for a shade of opposite extreme the relay 32 will operate slowly to open and close its con tact 33.

The tuning fork 34 when set in vibration induces a correspondingly varying electromotive force in the winding 35, which, applied to the grid 36 of the audion whose plate is 31, generates a plate circuit current of corresponding frequency that goes to the transformer primary winding 38 and to the electromagnet 39 to sustain the vibration of the tuning fork 34.

The secondary current induced by the current in the'primary 38 goes to the amplifier 40 from which lead two output circuits 4| and 42. .The output'over the circuit 4| goes to drive the synchronous motor I!) which drives the drum M, as already described. The circuit 42 comprises the contact 33 of the relay 32; already described,

and when this contact is closed at 33 the output from the amplifier 40 in the circuit 42 goes to the tuning fork 34.

the harmonic producer 43 which generates a harmonic and delivers this harmonic through the filter 10 to the amplifier 44 whose output then goes to energize the sending antenna 45.

It will be seen that the sending antenna 45 radiates wave trains of the wave frequency determined by the harmonic producer 43, and that these wave trains are of a variable length and have a variable frequency determined by the opening and closing of the contact 33 of the relay 32, and that the rate of opening and closing of this contact varies in accordance with the change in the shade of the elements of the picture passing across the path of the beam of light from the mirror l3 to the photoelectric cell 16.

At the receiving station the radio waves are received by the antenna 46, and the corresponding currents go through the amplifier 41 to the detector-amplifier 49. The input circuit for the detector-amplifier 49 comprises the secondary winding of a transformer 48 through which the locally generated current of standard frequency is applied for detection according to the hetero dyne method.

As will be explained presently, the output from the detector-amplifier 49 will be a current of the same frequency as that determined by the sending fork 34 at the sending station. Ihis output goes through the filter 50 and thence through the circuit 5i comprising the relay magnet 52 and the primary winding of the transformer 58. The relay 52 operates whenever the wave trains start or stop and shifts the recording stylus 53 accordingly. This is in engagement with a receiving surface wrapped on the drum 54. This drum 54 is driven by a synchronous motor 51 and traversed axially by the screw-threaded engagement of its shaft 55 with the frame 56. As will be pointed out presently, the speed of the synchronous motor 51 is such that the drum 54 is rotated and traversed in correspondence with the drum l4 at the sending end.

The same current that operates the relay 52 is applied through the transformer 58 to establish a correspondingly varying electromotive force on the grid 59 of the audion whose plate is 60. Accordingly the output current from this audion will vary at the same frequency, and it is applied through the magnet 62 to vibrate the tuning fork 63, and, as will be pointed out presently, the rate of vibration of the tuning fork 63 will be the same as of the fork 34 at the sending station.

The output current from the plate also goes through the amplifier 6| to two circuits 65 and 66. The circuit 65 supplies the current to the synchronous motor 51 already mentioned, and thus this motor is driven in synchronism with the motor l9 at the sending station.

The other output circuit 66 from the amplifier 6| goes to the harmonic producer 6'! which generates a certain harmonic of the fundamental frequency and applies it through the filter 68 and the transformer 48 to the detector-amplifier already mentioned. 5

By adjustment at 64 the rate of the tuning fork 63 is made very nearly the same as that of Suppose the rate of the tuning fork 34 is 1,500 cycles per second and that the harmonic producer 43 gives the thirty-eighth harmonic, which would be a current of frequency 57,000 cycles per second. Assume that the frequency that is getting through to the amplifier 6| is 1,500 cycles per second, and accordingly this is the frequency of the input to the harmonic producer 6! at the receiving station. Let the harmonic here generated be the thirty-seventh harmonic, a current of frequency 55,500 cycles per second. This frequency applied through the transformer 48 in the detector-amplifier 49 will give an output thereat of 1,500 cycles per second. Now suppose that the frequency of the receiving tuning fork 63 varies slightly from 1,500-and becomes 1,500in. The thirty-seventh harmonic of this frequency from the output of the harmonic producer 6! will be 5550013711, and the corresponding output frequency from the detector-amplifier 49 will be Therefore, it is evident that when the frequency of the fork 63 varies slightly from that of the fork 34, the variation in the frequency impressed upon the fork 63 will be in the opposite sense, thus establishing a tendency to 53 at the standard frequency determined by the fork 34.

In Fig. 3 an enlargement is shown for a received picture of a cube. This shows how the dark shades are obtained by rapid vibration of the recording stylus 53 and how light shades are obtained by slow vibration of this stylus. If the received record is too coarse-grained to be satisfactory, it can easily be photographed down to a smaller size, so that the observer will get only the impression of the varying shades without the details of the half tone structure.

It will be observed that the recording stylus always operates with the same amplitude, and it is this which prevents an unfavorable effect inthe reproduction due to variable transmission losses, fading, etc. which cause changes in amplitude, or level, of the received current. By utilizing variations in frequency to represent the shades of the picture, the response of the receiving device, or device for controlling the reproduction, need not vary in amplitude. By maintaining the amplitude constant the effect of change of amplitude or level of the incoming current upon the reproduction is eliminated.

I claim:

1. In a system for the transmission of images by radio, a source of constant frequency alternating current, image scanning means, means responsive to areas of the scanned image to produce variations in the frequency of the constant frequency source, a source of carrier waves of radio frequency, means energized by alternating current from said source of alternating current and having no control over said source for interrupting the waves of carrier frequency and means responsive to these interruptions for producing a record the density of which varies in accordance with the frequency variations.

2. In a system for the transmission of images by radio, light responsive means for testing the shades of the elemental areas of a picture, an alternating current generator, means responsive to variations in said light responsive means for causing a corresponding variation in the frequency of the current produced by the generator, means for generating a carrier current, means energized by, but having no control over, said alternating current to interrupt the carrier current in accordance with the frequency variations of said alternating current, and means responsive to the interrupted carrier current for reproducing said picture.

3. In combination, means hold the fork for testing the 7 shades oi the elemental areas of a picture or field of view, an alternating currentgenerator; means produced by said generator, a second alternating current generator, means for beating the current produced by said second generator with the current of varying frequency produced by 10 said first generator to produce a beat frequency current, means for generating a carrier current,

means to interrupt the carrier current by said of a picture, a generator 'for generating an al- 2 ternating current of a normal constant ireqnency, means to variable reactive means for confirm-King in acooriiience mm the light activation or said device the ow said reactive means mmrmtinmidifllmed 1 cgrail:fairies carp minimums, m

M w: m the M mncmmstmmsmcmgmm f ins device in accordance with said change in amplitude.

9. The method of producing an image at a receiving station of an object or field at a trans-V mitting station which comprises producing a 5 carrier wave separated into groups and having wave group frequencies corresponding to the tone values of elemental areas of the object or field, both the duration of the wave group and the intervals between successive wave groups 10 varying in the same direction in accordance with tone value variations; and causing an image producing action at the receiver at both the he ginning and end of each received wave group.

10. The method of carrier current image trans- 5 mission which comprises generating and trens= mitting a carrier current for predetermined periods and interrupting the transmission tor predetermined periods between successive transmission periods to represent a predetermined tone value or the image, and v rying ms the 1 on periods and the mtermption he in the same direction to represent a tone mine tmn said n w: time value. 25

ill. The method, or are image at a smidcnofanzohiectorfiehilatatrnnswithing at a carrier were at cement anrsiiinde tormemtacertaintone'tnmeeteimrpiien the tone white mm in and decsenwg hath the and the. periods of intermeme dim-mm,

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